1. Field of the Invention
The present invention generally relates to the transmission and reception of a digital signal, and, more particularly, to a receiver that identifies the interleaver mode of the received digital signal.
2. Background of the Invention
For the transmission and reception of a digital signal containing video, sound, data services, and the like, exemplary standards such as Digital Video Transmission Standard for Cable Television, DVS-031 Rev. 2, Society of Cable Telecommunications Engineers, May 1997 (SCTE DVS-031) and ITU-T Recommendation J.83 Annex B, April 1997 (ITU-T J.83B) are used. In particular, SCTE DVS-031 describes the adopted standard for digital cable in the U.S. When a digital signal is encoded using one or a similar standard as cited above, a Forward Error Correction (FEC) stage at the transmitter end is used for encoding the digital signal. Within the FEC stage, the digital signal is generally subjected to a convolutional interleaving operation that may occur between a Reed-Solomon (RS) block coding operation and a randomizer operation, as in the U.S. digital cable standard. The FEC stage helps enable the correction of random and burst mode induced errors when the encoded digital signal is modulated and transmitted through a communication channel such as the terrestrial airwaves or cable.
When performing an interleaving encoding operation, an interleaving mode may be selected from several interleaving modes, each mode representing a different process for interleaving a digital signal. When the encoded digital signal is transmitted and eventually received at a receiver, identification information (i.e., a control word) embedded in the received signal identifies the interleaving mode used to encode the digital signal. As in the U.S. digital cable standard, such identification information may be located within frame synchronization sequence trailers that delineate FEC frames contained within the encoded digital signal.
In an environment where a received digital signal is subjected to noise, the accurate identification of a selected interleaving mode becomes difficult. This problem is especially true in low signal to noise ratio (SNR) environments where the determination of a selected interleaving mode becomes very unreliable due to the presence of noise.